Method and device for monitoring a fuel-metering system

ABSTRACT

A method and a device for monitoring a fuel-metering system, in particular a common-rail system for a diesel fuel engine. A defect is recognized on the basis of an output signal from a structure-borne noise sensor.

FIELD OF THE INVENTION

The present invention, a continuation of PCT/DE96/00737 dated Apr. 27,1996, relates to a method and a device for monitoring a fuel-meteringsystem.

BACKGROUND INFORMATION

A method and device of this type are disclosed by U.S. Pat. No.5,241,933. It describes a method and a device for monitoring ahigh-pressure circuit when working with a common-rail system. In thecase of the device it describes, the pressure prevailing in the rail isregulated. If the manipulated variable of the pressure control loop liesoutside of a specifiable range, the device recognizes the existence ofan error.

In addition, devices are known, where the existence of an error isinferred on the basis of the pressure prevailing in the rail. Thepressure is thereby compared to lower and upper limiting values, and theexistence of errors is recognized when the pressure lies outside of thespecified range of values.

The drawback of these arrangements is that an error is first recognizedin response to a substantial pressure drop.

SUMMARY OF THE INVENTION

Given a device and a method for monitoring a fuel-metering system, theobject of the present invention is to be able recognize the existence oferrors in the most reliable and simple manner possible.

The method and device according to the present invention make itpossible for errors in the metering system to be recognized reliably andsimply. In particular, it is possible to reliably verify defectiveinjectors in common-rail systems.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a block diagram of the device according to oneembodiment of the present invention.

FIG. 2a illustrates signals from a structure-borne noise sensor plottedover time according to one embodiment of the present invention.

FIG. 2b illustrates signals from a structure-borne noise sensor plottedover time, given a faulty injector in the second cylinder, according toone embodiment of the present invention.

FIG. 2c illustrates signals from a structure-borne noise sensor plottedover time when no fuel is injected into the second cylinder, accordingto one embodiment of the present invention.

FIG. 3 illustrates a flow chart of the method according to oneembodiment of the present invention.

FIG. 4 illustrates a schematic representation of an internal combustionengine incorporating one embodiment of the present invention.

FIG. 5 illustrates a block diagram of the signal evaluation methodaccording to one embodiment of the present invention.

FIG. 6a illustrates the cylinder pressure plotted over time according toone embodiment of the present invention.

FIG. 6b illustrates the output from a needle motion sensor plotted overtime according to one embodiment of the present invention.

FIG. 6c illustrates the output from a knock sensor plotted over timeaccording to one embodiment of the present invention.

FIG. 6d illustrates the output signal from a band pass filter plottedover time according to one embodiment of the present invention.

FIG. 6e illustrates the output signal from a band pass filter plottedover time according to one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The device according to the present invention will now be elucidatedbased on the example of a self-ignition internal combustion engine, inwhich the fuel metering is controlled by means of a solenoid valve. Thespecific embodiment of the present invention shown in FIG. 1 relates towhat is known as a common-rail system. However, the procedure inaccordance with the present invention is not limited to these systems.It can be employed in all systems where such a fuel metering ispossible.

Element 100 denotes an internal combustion engine, which is suppliedwith fresh air via an intake line 105 and which emits exhaust gas via anexhaust pipe 110.

The illustrated internal combustion engine is a four-cylinder internalcombustion engine. Assigned to each cylinder of the internal combustionengine are injectors 120, 121, 122 and 123. Fuel is metered to theinjectors via solenoid valves 130, 131, 132 and 133. The fuel arrivesfrom what is known as a rail 135, via injectors 120, 121, 122 and 123 inthe cylinders of the internal combustion engine 100.

The fuel in rail 135 is pressurized to an adjustable pressure by ahigh-pressure pump 145. The high-pressure pump 145 is connected via asolenoid valve 150 to a fuel-supply pump 155. The fuel-supply pumpcommunicates with a fuel supply tank 160.

An electric fuel pump or a mechanical fuel pump can be used as afuel-supply pump. The use of an electric fuel pump requires apreliminary filter. Due to the high fuel temperatures, the electric fuelpump is preferably arranged in the vicinity of the tank. This results inlarge volumes between the electric fuel pump and the high-pressure pump,and substantial and, thus, long switch-off times. A rapid reduction inpressure, especially in the event of an error, can only be effected withadditional outlay.

These disadvantages are not associated with a mechanical auxiliarysupply pump arranged near the internal combustion engine. In the case ofthe mechanical auxiliary supply pump, solenoid valve 150 (also referredto as a shutoff value) is additionally necessary, which in case of anerror prevents the fuel from being supplied to the high-pressure pump145. Shutoff valve 150 can be optionally designed as a separatestructural unit. However, it can also be integrated, on the intake side,in high-pressure pump 145 or, on the delivery side, in auxiliary supplypump 155.

Valve 150 includes a coil 152. Solenoid valves 130, 131, 132 and 133contain coils 140, 141, 142 and 143, which can each receive current bymeans of an output stage 175. Output stage 175 is preferably arranged ina control unit 170, which drives coil 152 accordingly.

Furthermore, a sensor 177 is provided, which detects the pressureprevailing in rail 135 and routes a corresponding signal to control unit170. Element 180 is a structure-borne noise sensor, which is mounted onthe engine at a spot that conducts well acoustically. Thisstructure-borne noise sensor applies a corresponding signal to thecontrol unit. In place of the structure-borne noise sensor, it islikewise possible to use an acceleration sensor or a knock sensor.

One embodiment of the device according to the present inventionfunctions as follows. The fuel-supply pump 155 delivers fuel from thesupply tank, via valve 150, to high-pressure pump 145. High-pressurepump 145 builds up a specifiable pressure in rail 135. Usually, pressurevalues of greater than 800 bar are reached in rail 135.

The appropriate solenoid valves 130 through 133 are driven by conductingcurrent through coils 140 through 143. The drive signals for the coilsthereby establish the beginning of injection and the end of injection ofthe fuel through injectors 120 through 123. The drive signals areestablished by the control unit in dependence upon various operatingconditions, such as the driver's desire, speed, and other variables.

When working with a common-rail system, such a sustained injection of aninjector can not be easily recognized with certainty, given a balancingof masses in the rail. This can lead to an unwanted increase in torqueat one cylinder and even cause destruction of the engine when the peakcylinder pressures or the permissible temperatures are exceeded.

With the aid of the structure-borne noise sensor or by means of anacceleration sensor, in accordance with the present invention, thevibrations emanating from the combustion chamber are detected andreprocessed by means of an evaluation circuit.

If the vibration of one individual cylinder deviates significantly fromthe remaining cylinders or from the expected value, then the inferenceis made that an error exists in the corresponding injector.

The output signal from the structure-borne noise sensor is plotted inFIGS. 2a-2c over the arc of crankshaft rotation. The output signal fromthe structure-borne noise sensor when all injectors are experiencing afaulty operation is plotted in FIG. 2a over the arc of crankshaftrotation. The metering into the first cylinder takes place within therange of the top dead center, i.e., at 0° arc of crankshaft rotation ofthe first cylinder. This leads during metering or during combustion to asignificant signal from the structure-borne noise sensor. Acorresponding signal occurs in response to combustion in the secondcylinder at 180° arc of crankshaft rotation, in response to combustionin the third cylinder at 360° arc of crankshaft rotation, and inresponse to combustion in the fourth cylinder at 540° arc of crankshaftrotation.

FIG. 2b illustrates the corresponding signal given a faulty injector ofthe second cylinder. The sound emission during the combustion in thesecond cylinder is noticeably prolonged. This indicates that theinjector of the second cylinder is not working properly. This injectoris in its open state for longer than intended.

In FIG. 2c, no fuel is injected into the second cylinder, which meansthe injector allocated to the second cylinder does not enable any fuelmetering.

The evaluation process for recognizing the error is illustrated by wayof example in FIG. 3. In step 301, the output signal from thestructure-borne noise sensor is detected when fuel is metered into thefirst cylinder Z1. Correspondingly, in step 300, the structure-bornenoise sensor signal is detected during combustion in the second cylinderZ2. In steps 302 and 303, the structure-borne noise sensor signal isdetected for cylinders Z3 and Z4. In step 310, the amplitudes of thefour signals are summed and divided by four. This yields the averagevalue M of the four structure-borne noise sensor signals.

In step 320, a counter I is set to 0 and increased by 1 in subsequentstep 330. Query 340 checks whether the difference between the amplitudeZi of the I-th cylinder and the average value M is greater than athreshold value S. If this is not the case, query 350 checks whether Iis greater than or equal to four. If this is not the case, then step 330follows again, or when I is greater than four, step 300 follows.

If query 340 recognizes that the amount of the difference between theamplitude of the I-th cylinder Zi and the average value M is greaterthan the threshold value S, then the existence of errors is recognizedin step 360 and appropriate measures are introduced.

The method delineated here was described based on the example of afour-cylinder internal combustion engine. By properly choosing theparameters, in particular that of I, the method according to oneembodiment of the present invention can also include internal combustionengines having different numbers of cylinders.

Optionally, not the amplitude of the signal, but rather the timeduration of the signal can also be evaluated for recognizing errors.

Another advantageous embodiment of the present invention is illustratedin FIGS. 4-6e. Schematically illustrated in FIG. 4 is a four-cylinderdiesel fuel engine having two structure-borne noise sensors 410 and 411,which are mounted so as to be acoustically conductive on the engine.Element 415 denotes a needle-motion sensor and 420 a cylinder-pressuresensor. Element 105 denotes the fresh-air pipes, and 110 the exhaustpipes.

In FIG. 5, the signal evaluation for the two knock sensors 410 and 411is illustrated as a block diagram. The output signal from the firstknock sensor 410 arrives via a propagation-delay correction 201 at acylinder selection 220. Accordingly, the output signal from the secondknock sensor 411 arrives via a second propagation-delay correction 202at cylinder selection 220.

From cylinder selection 220, the signal arrives at a first band pass 210and at a second band pass 215. The output signals from the band passesarrive at a signal processing 230, which in turn applies signals to avalve-timing unit 240. Furthermore, output signals from band passes 210and 215 arrive directly at engine timing 240. Furthermore, signalprocessing 230 processes signals from various sensors 235.

This device functions as follows: the propagation delay of the diversesignals from a signal source to the different knock sensors 410 and 411varies. This propagation delay is compensated by the propagation delaycorrections 201 and 202. On the basis of the signal height, which inturn is a function of the distance between the signal source and thesensor, the cylinder recognition assigns the signal to a specificsensor. This enables an allocation to be performed between the detectedsignal and the corresponding cylinder.

In principle, the procedure described in the following can also becarried out with a structure-borne noise sensor. The signal quality canbe substantially improved when of two or more structure-borne noisesensors are used. It is especially beneficial for the structure-bornenoise sensors to be arranged at spatially different installation siteson the engine. By summing the signals that have been corrected forpropagation delay, the useful signal can be substantially increased incomparison to spurious signals.

The present invention provides for the first band pass to have breakfrequencies of 10 kHz and 30 kHz. The second band pass 215 has breakfrequencies of 500 Hz and 4 kHz. These frequency values merely representrecommended values, and they can vary depending on the type of internalcombustion engine.

The band passes filter the output signals from knock sensors 410 or 411.On the basis of the filtered signals, the signal processing definesdifferent variables which characterize the injection or combustion. Thethus obtained signals are used by the engine timing for the open andclosed-loop control of the internal combustion engine.

Plotted over time in FIG. 6a is the cylinder pressure, in FIG. 6b theoutput signal from the needle-motion sensor; in FIG. 6c the outputsignal from one of the knock sensors; in FIG. 6d the output signal fromthe first band pass; and in FIG. 6e the output signal from the secondband pass. In response to the small quantities for the preliminaryinjection, the valve needle generally does not open up to the top limitstop.

In the case of the preliminary injection, one can merely perceive theneedle hitting against the lower limit stop at the end of the injectionprocess. At this instant, the amplitude of the output signal from theknock sensor rises. Also at this instant, the high-frequency componentsof the output signal from the knock sensor increase. This instant isdesignated VE.

At the beginning and end of the main injection, the needle of theneedle-motion sensor moves to the lower or to the upper limit stop. Atthese instants, the amplitude of the output signal from the knock sensorand, in this case, in particular the high-frequency components rise.This instant is designated as HE.

The beginning and end of the main injection are recognized when theneedle of injectors 120 through 123 moves during opening operation up tothe upper limit stop and during closing operation to the lower limitstop. These instants are recognized on the basis of the output signal'srise from the first band pass over a first threshold value. If theinjector needle's hitting is not recognized, or if it is not recognizedwhen the injector is closing, then this is evidence of a sustainedinjection.

Based on these signals, the decision is made during every injectionwhether a sustained injection is taking place or not. The monitoringpreferably follows individually for each cylinder. When a specifiablenumber of sustained injections is recognized for one cylinder, this isevidence of a defect.

If the fuel-supply pump is designed as a mechanical auxiliary supplypump, for example as a gear pump, then there is no actual way tointerrupt the delivery of fuel by means of the auxiliary supply pump,since it is driven directly by the engine. Therefore, the presentinvention provides for the fuel delivery from auxiliary supply pump 155to high-pressure pump 145 to be interrupted by means of the electricalshutoff valve 150 between auxiliary supply pump 155 and high-pressurepump 145.

When an error is recognized, valve 150 interrupts the supply of fuel tohigh-pressure pump 145. An error can be recognized in this case, forexample, using the described procedure. However, other methods forrecognizing errors are feasible.

If valve 150 is designed as a 2/2 valve, i.e., it blocks the flowbetween auxiliary supply pump 155 and high-pressure pump 145, then apressure builds up upstream from the valve when the valve is closed.Appropriate measures are provided to avoid this pressure build-up. Forexample, a relief valve can be integrated in the auxiliary supply pump.Alternatively, the shutoff valve can be designed as a 3/2 valve. In sucha case, when valve 150 is driven, the fuel arrives via a line, drawn inwith a dotted line, from auxiliary supply pump 155 directly back in fuelsupply tank 160. The need has been eliminated in this alternativeembodiment of the present invention for a relief valve in auxiliarysupply pump 155.

What is claims is:
 1. A method for monitoring a metering system in anengine which includes a plurality of cylinders, wherein a fuel flow isdelivered by at least a first pump from a low pressure area to a highpressure area, the method comprising the steps of:generating an outputsignal from a structure borne noise sensor for each of the plurality ofcylinders; computing an average value of the output signals from theplurality of cylinders; and recognizing a malfunction in the meteringsystem when the output signal of a particular cylinder deviates from theaverage value B.C. Mode than a specified value.
 2. A method formonitoring a metering system in an engine which includes a plurality ofcylinders, wherein a fuel flow is delivered by at least a first pumpfrom a low pressure area to a high pressure area the method comprisingthe steps of:generating an output signal from a structure borne noisesensor for each of the plurality of cylinders, the output signal havinga time duration; computing an average time duration of the outputsignals from the plurality of cylinders; and recognizing a malfunctionin the metering system when the time duration of the output signal for aparticular cylinder deviates from the average time duration by more thana specified value.
 3. The method of claim 1, wherein each of theplurality of cylinders has an injection period, and further comprisingthe steps of:filtering the output signal to generate a filtered signal;and determining one of a beginning of the injection period and an end ofthe injection period as a function of the filtered signal; generating asignal indicative of one of the beginning and end of the injectionperiod; and wherein the malfunction is recognized for one of theplurality of cylinders as a function of the signals indicative of one ofthe beginning and end of the injection period.
 4. The method of claim 3whereinthe malfunction is recognized when a delay between the signalindicative of the beginning of the injection period and the signalindicative of the end of the injection period attains a specified delayvalue.
 5. The method of claim 1, wherein the recognized malfunctionincludes a defect in a solenoid valve.
 6. The method of claim 1, whereinthe recognized malfunction includes a defect in a fuel injector.
 7. Amethod for monitoring a common rail fuel metering system in a dieselfuel engine, wherein a fuel flow is delivered by at least one auxiliaryfuel pump from a low pressure area to a high pressure area, comprisingthe steps of:recognizing a malfunction in an operation of the fuelmetering system; and stopping the fuel flow between the auxiliary pumpand a high pressure pump when the malfunction is recognized.
 8. Amonitoring device for an engine, comprising:a fuel metering systemincluding at least one pump, the at least one pump including at leastone auxiliary supply pump and a high pressure pump, the at least oneauxiliary pump delivering a fuel flow from a low pressure area to a highpressure area; a sensor attached to the engine, the sensor including oneof a structure borne noise sensor and an acceleration sensor, the sensorgenerating an output signal; an evaluation circuit coupled to thesensor, the evaluation circuit recognizing a malfunction in the meteringsystem when the output signal deviates from a specified value; and meanscoupled to the fuel metering system to prevent the fuel flow from theauxiliary pump to the high pressure pump.
 9. The device of claim 8,wherein the engine includes a diesel fuel engine and the fuel meteringsystem includes a common rail fuel metering system.